Method for automatically controlling transfer voltage in printer using electrophotography system

A method of photocopying onto recording media of varying materials, comprisin:

• feeding said recording media from a feeding tray;
• conveying said recording media through a first sensing unit that activates a second sensing unit to be operational;
• conveying said recording media through said second sensing unit that detects whether said recording media is made of paper or is a transparency;
• conveying said recording media through an image forming unit by having said recording media proceed between an electrically charged photosensitive drum containing a toner image and a transfer charger, wherein a potential difference between said photosensitive drum and said transfer charger depends on whether said second sensing unit detects said recording media as a transparency or as a sheet of paper;
• bonding said toner image to said recording media;
• and
• discharging said recordingmedia containing said image from said image forming unit.

An electrophotographic device for printing images, comprising:

• a photosensitive drum;
• a charging unit to uniformly charge said photosensitive drum;
• an exposing unit to expose said photosensitive drum and to produce a latent image on said photosensitive drum;
• a developing unit to deliver toner to said photosensitive drum forming a toner image on said photosensitive drum over said latent image;
• a transfer charger to transfer said toner image from said photosensitive drum to a sheet of recording medium;
• a fixing unit for fixing said toner image to said recording medium;
• an automatic feed tray to allow automatic feeding of individual sheets of recording medium into said electrophotographic device;
• a recording medium conveyance path located between said automatic feed tray and said photosensitive drum for transporting sheets of recording medium from said automatic feed tray to said photosensitive drum;
• a first sensing unit located on said conveyance path to determine the location of said sheet of recording medium;
• a second sensing unit located on said conveyance path, activated in response to said sheet of recording medium passing said first sensing unit, to detect whether said recording medium is made of paper or is a transparency, said sensing unit generating a first signal if said sheet of recording medium is a transparency;
• a transfer voltage generator for applying one of a first and second voltages to said transfer charger;
• a video controller for generating a print command;
• and
• an engine control unit for generating, in response to said print command, a first control signal when said first signal is not received from said sensing unit, and for generating, in response to said print command, a second control signal when said first signal is received from said sensing unit, said voltage transfer generator applying said first voltage to said transfer charger to transfer said toner image onto said recording medium in response to reception of said first control signal, said voltage transfer generator applying said second voltage to said transfer charger in response to reception of said second control signal.

A method of photocopying on a sheet of recording media made of either paper or transparency material, comprising:

• feeding said sheet of recording media from a feeding tray;
• sending a print command to a video controller;
• relaying said print command from said video controller to an engine control unit;
• allowing said sheet of recording media to be conveyed past a first sensing unit, said first sensing unit sensing passage of said sheet of recording media;
• when said first sensing unit senses passage of said sheet of recording media enabling a second sensing unit, said second sensing unit detecting whether said sheet of recording media is normal paper or is a transparency;
• allowing said sheet of recording media to be conveyed past said second sensing unit located adjacent to said feeding tray;
• outputting from said second sensing unit to said engine control unit a first signal in response to the passage of a transparency past said second sensing unit;
• outputting from said engine control unit to a transfer voltage generator a second signal in response to receipt of said first signal from said second sensing unit;
• outputting a first voltage bias by said transfer voltage generator to a transfer charger in response to said second signal received from said engine control unit;
• producing a latent image on a photosensitive drum by said engine control unit;
• producing a toner image on said photosensitive drum by introducing toner;
• conveying said sheet of recording media between said transfer charger and said photosensitive drum, transferring said toner image onto said sheet of recording media;
• conveying said sheet of recording media between heated and pressurized rollers to fix said toner image to said sheet of recording media;
• and
• discharging said sheet of recording media containing said image from said electrophotographic device.

An electrophotographic device for printing on sheets of recording medium made of either transparency material or paper, comprising:

• means for inserting into said device said sheets of recording medium;
• means for signaling to a controller of said electrophotographic device that a printing operation is about to be performed;
• means for enabling a first sensor that senses passage of said sheets of recording medium;
• means for enabling a second sensor in response to said first sensor sensing passage of said sheets of recording medium, said second sensor determining whether said sheets of recording medium are transparencies;
• said second sensor for signaling to said controller of said electrophotographic device that said recording medium is a transparency;
• means for adjusting a transfer voltage based on said signals received by said controller of said electrophotographic device;
• means for transferring an image from a video control unit to a printing engine in said electrophotographic device and then on to said sheets of recording medium;
• means for fixing said image onto said sheets of recording medium;
• and
• means for discharging said recording medium from said device.

A method of automatically controlling transfer voltages of a printer in an electrophotography system having a first recording media sensing means for determining if a sheet of recording media is conveyed to an image forming unit and a second recording media sensing means, comprising the steps of:

• enabling said second recording media sensing means upon activation of said first recording media sensing means;
• generating said second recording media sensing signal while said sheet of recording media is being conveyed to said image forming unit when said first recording media sensing signal is received from said first recording media sensing means under the control of a central processing unit of the printer;
• and
• when an overhead projector (OHP) transparency is being conveyed to the image forming unit, setting a voltage to a level that is preestablished for toner image transfer onto OHP transparency in response to an OHP transparency sensing signal produced by said second recording media sensing means, and when a normal paper is being conveyed to the image forming unit, setting a voltage to a level that is preestablished for toner image transfer onto normal paper for printer performance.

A method of automatically achieving optimum image density during an electrophotographic duplication process when various recording medium are used, comprising:

• feeding a sheet of recording medium into an electrophotographic machine;
• conveying said sheet of recording medium along a conveyance path;
• detecting, during the conveyance, said sheet of recording medium;
• when said sheet of recording medium is detected, enabling a sensing means that determines whether or not said sheet of recording medium is a sheet of paper or a transparency;
• detecting, during said conveyance, whether or not said recording medium is a sheet of paper or is a transparency;
• continuing to convey said sheet of recording medium to an image forming means;
• applying a transfer voltage bias whose magnitude depends on whether said sheet of recording medium is detected as being a sheet of paper or a transparency;
• transferring an image from said image forming means onto said sheet of recording medium;
• and
• ejecting said sheet of recording medium from said electrophotographic machine.